Heating apparatus



I l l I I I I l I I I I I I I I I I I I II I I Filed Sept. 24, 419.30

2 Sheets-Sheet l Oct. 16, 1934. E. F. NORTHRUP HEATING APPARATUS FiledSept. 24. 1950 2 Sheets-Sheet 2 M0/magy. Y

UNITED STATES PATENT OFFICE l HEATING APPARATUS Edwin man Nal-tmp,Princeton, N. J., signor to Ahx Eleetrothermic Corporation, Ajax Park,

N. J., a corporation ot New Jersey Appunti september 24, 1930, serialNo. 484,121

19 cmnml.L (c1. 21e-13) My invention relates tothe inductive heating ofmetallic sheets or plates.

One purpose of my invention is to inductively heat a resistorilnulllehaving a secondary current path passing about more than one mullle Afurther purpose is to heat interior walls of a resistor muille byinduced current conducted from the point of induction through theinterior walls. A

A further purpose is to induce electric current in the outside walls ofa muille and to pass the current through the partition walls betweencompartments in the mullle.

. A further purpose is to provide a tortuou or serpentine secondarycurrent path whose convolutions include a plurality of mume compartmentswithin which heating is effected.

A further purpose is to interrupt the edge of an induction furnaceresistor secondary in order to require that the induced current travelthrough a longer path to utilize the additional heating effect secured.Y

A further purpose 'is to provide parallel compartments having wallsforming a heating resistor for the compartments, and to induce currentin the compartment walls, spacing parts of the separating walls to causethe current to travel on both sides of the spacing in order 'to heat theentire wall.

A further purpose is to longitudinally slit a partition wall between twoparallel compartments which are to be heated electrically so thatelectric current induced in the walls of the compartments may lbe causedto traverse a path about'the slit, increasingthe resistance whileavoiding increase in the secondary reactance.

A- further purpose is to utilize not only the sides but the end oi amunie as an electrical resistor in which heat is generated throughvinduction of `electric current,

A further purpose is to interrupt the continuity of the enJd ofa'resistor mullle in which current is induced so that the end of themutlle may be heated by l es;

interruption. Y f

A further purpose is to inductively heat a plurality of electricalresistors forming a mule compartment, one resistor being axially aboveanother, and desirably to change the number of resistors used accordingto the dimensions of the charge. Y

A further purpose is to make up a multiple l compartment muille fromseparate resistor 66- e on both sides of the tions, each including partof all of the mule walls.

A further purpose isl` to vertically insert a plurality of chargesconcurrently within a plu-v rality of parallel chambers in a muiiie.

A further purpose is to use a common closure for the charge-insertingends of a plurality of parallel muffle chambers.

A further purpose is to bell a plurality of mulle compartments so as tovretain gases lighter than air within the compartments and to insert thegas preferably after thel charge has been applied.

Further purposes will appear in the specification and in the claims.

My invention relates to the processes involved as well as to apparatusby which the processes can be carried out.

I have preferred to illustrate one main form only with modifications,selecting a form which is practical, efficient and highly advantageousbut which has been selected primarily because it illustrates to the bestadvantage the principles involved.

Figure 1 is a. broken transverse section partly in elevation, showingthe parts of one form of my construction ready for operating assemblageby insertion of the charges. Y

Figure 2 is a broken top plan View of one resistor section used inFigure 1.

Figure 3 is a broken section of Figure 2 taken upon line 3--3.

Figures 4, 4a and 4b are broken top plan views corresponding to Figure 2but showing modflcations.

Figure 5 is a fragmentary section upon line 5--5 in Figure 4, slightlymodified by omission of the dowel, and having added a vview of the nextmuile section with electrical insulation between the sections.

Figure 6 is a broken bottom plan View or the muille end section shown inFigure 1.

' Figure 7 is a broken section taken upon line l 7-7 of Figure 6.

In the drawings similar numerals'indicate like but adaptation of the.invention to meet thel ing. Unequal heating is likely to cause bucklingof the plates.

At the present time the heating of steel sheets for use in automobilebodies requires about 18 hours in one typical installation.

My invention is excellently suited to heating sheets of this characterquickly and uniformly;

exacting requirements of this particular work does not mean that theinvention is unsuited to other heating applications.

Aside from annealing there are not only numerous other purposes forwhich relatively broad and thin metal must be heated, as, for example,preliminary to stamping and forming operations, but other objectsrequire heating for the same and for other purposes.

I have discovered that induced current may be applied to great advantagefor such heating o'not only fiat sheets and plates but such deformedsheets or plates nested or individually and also to the heating ofobjects of regular or irregular contours.

however, -that any suitable shape of charge is included within thisdesignation, the muille compartments merely being made to conform to thedimensional requirements of the particular product to be heated.

By my invention I inductively apply current `to a resistor comprisingthe mume walls. As

` thegdepth of penetration'of the flux is relatively short, and as goodcoupling is required, substantially all of the induced current will bedeveloped in the periphery of the resistor.

I have therefore provided artiiicial means for conducting the inducedcurrent from the peripheral point at which it is developed into theparts of the munie which are not directly accessible to the induction.For this 4purpose I provide an electrically conducting path fordiverting the induced current into the interior of the mume,particularly into the partitionwalls between individual munie chambers..

Aside from the resistance heating of the interior parts of the muile,the elongated current path through these interior parts has certainadvantages not at ilrst apparent. In the ilrst place, this pathincreases the resistance of the secondary circuit, thus causing acertain amount of RP heating in the elongated path.

Furthermore, the maximum power will be absorbed by a secondary when thesecondary resistance equals the secondary -r'eactan'cel Since in.V mypartition walls tlm current on opposite sides of the walls is -ilowingin opposite direction,'the` path through the partition walls issubstantially non-inductive and does not tend to increase the secondaryreactance. It will however increase the secondary resistance, and as thereactanceis ordinarily more than the resistance, will improve the powerconsumption.

I ndit convenient to build up my mume of a plurality of inductivelyheated resistors placed one upon another. Since, when these are properlyregistered, adjacent parts ofadjacent resistors will be at the samepotential, no tion need be placed between resistor sections. When the.dimensions of the charge sheets are increased in'two directions beyondthe maximum 80 chamber dimension of the munie section, I will then beobliged to Aemploy new mullle sections.

Sinceinmanycasesthechargewillsuffer from oxidation, I will ordinarilyemploy a protecting orireatingahnosphereinmymumeto avoid injury to thecharge.

Describing the structure of Figurel in illustration and not inlimitation v I have showna multiple 'compartment muille 10 made up ofsections 11 between which no dif- 90 ference of potential is intended toexist and which are therefore rested one upon another, being quickly andeasily alined by means of dowels andY openings 12, 12'.

The mume is shown as bottom-loading at 13 95 and forthis upon aplatform14having an opening 15. About the munie and upon the platform I placeVan inductor coil 16 supplied with current from any suitable source 17.Conventional power factor correction is shown by condensers 18. At thetop the munie is closed by a cover 19.

Electrical insulation for the coil' is shown at 20.Thisatthesametimeactsasaretaining wall, if such be needed, for a nelydivided 105 heatA insulator 21 which may be poured into the space andover the combination mullle. Because oftheuseofslitsorcutsinthemulllecover, afterwards discussed at length, I use strips 22 ,to prevent the-nely divided material from passinglntothecompartments 23, 24and25ofthe.mume. ThevariouspartsofFigurelareconventionally, divided at the middleby broken lines 26 to indicate that the number of compartments may beincreased if desired.

Thenelydividedmaterialusedmaybeany suitable heat insulator of whichZircon sand is a good example, but of which diatomatiousearth-onsaleunderthe nameofsilocel-isthe best example known to me. 120

It is desirable though not necessary to use a heat insulating top abovethe finely 'divided refractormwhichtoplshowatm. Thisisin-'Wheremetalsheets29ofsteelorironforexamplearetobeheatedtheyarepreferablybaledandtied at.30 andarerestedupontheiredges onabottomclosure3lwhichultimatelyiits into 130 theopeningllntheplatfomsealingtheopcning.'lhis closure is effected by lifting the bot. tom 31 by means ofplungers 32 of hydraulic elevator cylinders 33 whichare shown ashavinginlet and outlet uid Supply and discharge con- Whether the'mume is madeup in a single section or is of unit construction as seen in Figure 1,my invention provides for heating not only the outside oi the muille,but also the interior partitions of the muiiie by current induceddirectly in the outermume walls and conducted through the partition. Isecure this highly desirableeffeet in practice by interrupting the e ofcurrent through the outer walls at the partitions and directing thiscurrent in series though one side of each partition, toward the oppositeouter wall, and back through the other side of each partition, theinduced current then continuing through the outer wall.

The detail of how this diversion of the current path is secured is notimportant to the broader aspects of my invention, which contemplates the'artificial extension of the -current path to pass through the partitionwalls in series with the outer walls. The most convenient way ofcarrying out the invention is to form a partition dit vided throughmost.A of .its length parallel to one of its surface planes andelectrically connected at the 'ends with the adjoining outer walls, sothat the entire partition is in series with the outer wall.

In Figure 2 there is shown one of the resistor sections such as areillustrated in Figure 1. This may be cast integrally whether thedivisions are cast in or cut in. 1

The muiiie chambers are separated by parti `tion walls 44 and 45. Eachof the walls 44 and 45 is separated interiorly at 46 or 47, dividing thepartition wall 44 into two conductors 48 and I 49 and likewise dividingthe partition wall 45 into two conductors 50and 51.

Remembering that the inductor coil surrounds the outer surfacev of theresistor, current will-be induced for `example in the outside conductor52 and likewise in the short end conductor 53 and will tend to flowaround the outside of the resistor. Due, however, to the separation 46,the secondary current will be compelled lto flow through the conductor48, then across vat 54 and finally back through the conductor 49 on theother side of the partition wall.

60 and 61 atxthe ends of the partition walls are In Figure 4b Iillustrate longitudinal partition separations 46z and 463 performing thefunction of the partition separation 46, and extending from oppositeends toward the interior to the area 54', where the separations cease.In this case 'the induced current will travel in from both sides of theouter wall through the partition wall, across at 54' and back throughthe opposite partition wall.

The separations 472 and 473 are similar to 46z and 463, and arediscontinued at 56 to permit the current to :liow from one side of thepartition wall to the opposite sidey of the partition wall.

In Figure 5 I illustrate fragments of two resistor sections 11 placedone above another and separated by electrical insulation 62. In thisgure I have omitted the dowel for insuring that the adjoining sectionsregister. 'Ihe insulation will then insure that points of diiferentpotential do not come into contact.

6 and 7 illustrate an end section for the munie. For convenience the endsection is domed at 63 to provide additional interior capacity for themuille. separations 464 and 47* correspond generally with the partitionseparations in the interior sections. In addition the centers of thedomes contain longitudinal separations 64 to insure that current willflow through the tops of the domes to heat them.

It will be evident that the relation between the resistance andreactance in the secondary circuit will be affected by the frequency,which must'therefore be considered to determine the difference between.the reactance and resistance when this difference is sought to `be madeup. The frequency selected will, of course, make a diiference in thedepth of penetration, requiring thicker walls for lower` frequency, thewalls being preferably not less in thickness than three times the depthof penetration and certainly not I less than twice the depth ofpenetration. It

must be remembered also that with higher frequency the heating effect isimproved at tem- This current and more current thereinduced'f'vpeltllres bOVe the decalesence point With iron will then flowthrough the end conductor 55, but

will be again diverted by the separation 47 of vthe partition wall 45,and will take the path through the partition conductor 50, across at 56and back through the opposite partition conductor 51 to the endconductor 57. The secondary circuit will then be completedthrough theoutside condurztors 58 and 59. V

It will beevident that the form of the resistor may be varied in anumber of ways immaterial to my invention. I have illustrated'a numberof thesevariations in Figures 4, 4a and 4b.`

In Figure 4 the separations 46 and 47 bear the same relation to theother structure as in Figure 2, but the partition wall has beenseparated at 60 and 61 from the end wall 59. Electrically I considerthis change of relatively little importance because it Adoes not vitallyalter the current path in the partition, which inany case will bethrough the partition conductors 48 and 49 or 50 and 51.

In Figure 4a I illustrate the partition separations 46 and 47 yextendingfrom opposite ends of the outside muiile wall. I also show a separationbetween the outside wall 59'and the partition Wall at 60, but nocorresponding separation at the opposite end of the other partitionwall. It will thus be seen that the separations outside walls of themuille close to the inductor coil lto build up an appreciable fiow ofcurrent and I' then conduct the current thus inductively produced intointerior walls of the muffle where I use it advantageously to heat partsin which it would not be possible directly to induce current. Y

I believe that I am the first thus to divert current induced in thewalls of a resistor muiile to be used for resistance heating elsewhere.

I believe also that I am the first to assemble an inductively heatedlymufile comprising a plurality of chambers from a series of units builtup one against another. I

It will be evident that I have provided not only an adjustable muilie ofunusualv adaptability and convenience both in ,manufacture and in usebut that I have madeaccessime for direct induction' the interior of: thestructures which hitherto have been inaccessible and which .have reliedfor their heat upon conduction from the exterio'r surface.

It will be evident `that there is a considerable advantage in couplingin having'the primary coil conform to the shape of the secondary and inspacing it uniformly from the secondary.

I nview of my invention and disclosure variations and modifications tomeet individual whim or particular need will doubtless become evident toothers skilled in the art, to obtainallor part vthe inductor havingpartition walls carrying current in series with current induced in theouter walls.

2. A resistor forming walls of a-muille adapted to be used with asurrounding primary coil and having interior partition wallselectrically in series with its outside walls.

- used with a surrounding inductor coil and having the resistance of itsoutside walls increased by articially lengthening the circuit pathwithin the interior of the muiile.A

4. A muille secondary resistor adapted to be used with -a surroundinginductor primary and having the length of its'secondary current bothartificially and non-inductively -increased at a distance from its outerwalls.

5. A secondary muiile' resistor 'adapted to Vbe Iused with a surroundinginductor coil and having the resistance of its outside wallsartificially increased byA including in series within their circuitpartition walls, the increase being non-- inductive and suiiicient-tomake the resistance .of the circuit approach the value of the reactanceso that the power consumption is increased.

6. Ina multiple secondary resistor having a plurality of compartments,outer electrically conducting compartment walls, and electricallyconducting interior partitionfwalls divided in the planes of the walls,each division being cut through .an outer wall.

7. A resistor muille secondary adapted to be used vwith a surroundinginductor primary and having interruptions in the surface of the resistor across the induced current path, providing an artificially extendedlength of secondary conductor path returningupon itself about theinterruption.

8. A muille havinga plurality of compartments and a serpentineelectrically conducting wall therefor, in combination with an inductorcoil surrounding the entire wall and inducing cur` rent through theconvolutions of the serpentine wall. Y

9. A resistor mutlle secondary for use with a 4 surrounding inductorprimary and having outer side and end walls and partitions betweenopposite walls to divide the munie into compartments and having thewalls from which the partitions spring and the partitions separated fora considerable distance toward the `opposite walls through the lengthsof. the partitions, whereby current'- nduced along the outer walls in adi- 3. A secondary muille resistor adapted to be rection across thepartitions will follow onepartition part at the separation to a point sup of separate sectionsdivided parallel to the current paths and eachapertured perpendicular to the division to form in the aggregatecompartments of adjustable height depending upon the number df sectionsused. 11.. A multiple compartment resistor mums secondary of adiustableheight having parallel compartments and comprising independent resistorsections divided transversely across the compartments.` Y

12. A resistor mume secondary section having a plurality of openingstransversely to the plane of the section corresponding with compartmentsto be built up from the sections and having the partitionvwalls betweenthe openings divided in the planes of the partition walls from side toside of the section parallel with the longer Ydimension of the openingsand from one terminal QO wall about the `opening nearly to the oppositewall.

1a. A; plurality Yof :nume secondary sections, each having a pluralityof openings transversely to the plane of the section correspondingf with105 compartments to be built up from the sections and having theinterior partitio'n walls between the openings divided in the planes ofthe par' tition walls from side to side of the section parallel with thelonger dimension of the openings 110 and from one terminal wall aboutthe opening nearly to the opposite wall and means for ensuring thatparts of one section do not engage parts of another section which have adifferent 14. A resistor mufileV end secondary adapted to closeaplurality of 'munie compartments and toreceive induced current from a;primary surrounding the mume,` having the walls of the mume end-separated inwardly from outside edge walls at intervals a substantialdistance toward an opposite edge in order-that current induced about theperimeter of the mume end will follow the line ot the separation to ajuncture point andbackagaintothesameedgeofthemume. 15. A multiplecompartment resistor munie secondary of adjustable height havingparallel compartmentsand comprising independent resistor sectionsdivided across the compartmentsopen at the bottom in combina--tionwithmeansforinsertingcharges from bneathlandaclosurei'orthebottomuponwhich 16. A multiple compartmentresistor munie secondary of adjustableheight having parallelcompartments and comprising independent resistor sections dividedtransversely across the compartments open at the bottom in combinationl*with means for inserting charges from be- Y neath, a closure forthebottom upon which the 1 charges rest, a closure'icr the top of themuille and means for inserting av vspecial atmosphere within the mume asa bell.

1'1. A redsun munie secondary of non-circular*A i ttons between themseparated through to the outer walls to artificially extend the path ofthe induced current so that the resistance' of the induced current atthe frequency selected will approach the reactance of the circuit.

19. A resistor munie secondary adapted for use with a surroundinginductor primary, having a plurality of compartments with interior

